The isolation of graphene (one atomic layer of carbon) (Novoslev et al., 2005, Nature 438:197-200) constitutes a new paradigm in materials exploration in which atomic layer control is possible, (Avouris et al., 2012, Int Electron Devices Meet 23.1.1-4) and even though graphene is considered transformational, it is only the “tip of the iceberg.” Synthesizing and heterogeneously combining atomic layered transition metal dichalcogenides (Wang et al., 2012, Nat Nanotechnol 7:699-712; Chhowalla et al., 2013, Nat Chem 5:263-75) to form van der Waals (vdW) heterostructures will be the ultimate route to tuning electronic and photonic properties. Recent advances in the synthesis of two dimensional transition metal dichalcogenide (TMDs) by methods such as powder vaporization (Lee et al., 2012, Adv Mater 24:2320-5; Lin et al., 2014, ACS Nano 8:3715-23; Huang et al., 2014, ACS Nano 8:923-30) and metal-organic chemical vapor deposition (MOCVD) (Eichfeld et al., 2015, ACS Nano 9:2080-7; Kang et al., 2015, Nature 520:656-60) have opened up new opportunities in the realization of two-dimensional (2D) electronics. However, there still remains a large challenge in the ability to synthesize uniform domains with controlled thicknesses and dimensions for large-scale device fabrication. In addition to vertical stacking of atomic layers to tune the optical and electronic properties, controlling properties of 2D materials can also be achieved by producing quasi-one-dimensional strips, known as nanoribbons.
Recently, heterogeneous integration of layered materials has been predicted to lead to completely new electronic properties (Terrones et al., 2013, Sci Rep 3:1549) resulting in a novel electronic material entirely different from the constituent layers. One such unique phenomenon that results from this heterogeneous stacking is a significant reduction in the energy bandgap compared to the constituent layers. These exciting predictions are just now beginning to be realized experimentally through manual stacking of different layers (Fang et al., 2014, PNAS 111:6198-202), and the development of bottom-up synthesis of such heterostructures is ripe for exploration.
Developing routes for templated growth will significantly enhance the ability to tune the electronic properties of these 2D materials, allow for improved morphological control, and simplify post-synthesis device fabrication. Nakada et al. first theoretically predicted a broad range of electronic properties is possible by changing the width and crystallographic orientation of the edges in a graphene nanoribbon, with properties ranging from tunable semiconductors to metals (Nakada et al., 1996, Phys Rev B 54:17945-61; Yazyev, 2013, Ac Chem Res 45:2319-28). Like graphene, TMD nanoribbons display extraordinary electronic and magnetic properties. Among TMDs, MoS2 is the most widely studied and provides evidence that nanoribbons can be very effective for tuning the properties of 2D materials (Li et al., 2008, J Am Chem Soc 130:16739-44). Armchair MoS2 nanoribbons are predicted to exhibit energy band gaps that vary with width and termination of edge atoms with hydrogen (Li et al., 2008, J Am Chem Soc 130:16739-44; Erdogan et al., 2012, Eur Phys J B 85:33), while zigzag MoS2 nanoribbons are ferromagnetic metals, and bare zigzag nanoribbons are half-metallic (Li et al., 2008, J Am Chem Soc 130:16739-44; Erdogan et al., 2012, Eur Phys J B 85:33; Pan and Zhang, 2012, J Mater Chem 22:7280). Furthermore, the adsorption of adatoms and creation of vacancy defects in MoS2 nanoribbons have crucial effects in the electronic and magnetic properties, where a net magnetic moment can be achieved through the adsorption of cobalt adatoms to the nonmagnetic armchair nanoribbons (Pan and Zhang, 2012, J Mater Chem 22:7280; Shidpour and Manteghian, 2009, Chem Phys 360:97-105).
There has been some success in achieving selective growth via specified pre-synthesis methods. The majority of methods utilize physical masks or templates for specific area growth inhibition, with a focus on synthesis of 1D nanowires to control wire placement. Templated growth utilizing physical masks of consumable materials that can be etched away post-growth have yielded ways for high throughput cost effective synthesis of nanowires, however, this leads to post-growth etching to remove the template material (Xia et al., 2003, Adv Mater 15:353-89). Physical modification of the substrate surface such as etching pillars or trenches in the surface to either confine or promote growth has also been demonstrated (Yamano et al., 2015, J Cryst Growth 425:316-21; He et al., 2005, Adv Mater 17:2098-102; Eichfeld et al., 2005 Nanotechnology 18:315201) but requires large amounts of pre- and post-growth fabrication and can ultimately affect the growth quality. Specific substrate surface functionalization as a process to induce selective growth have also been described. Lloyd et al discussed using UV radiation to decompose the surface to allow for a better seed layer for ZnO nanowires (Lloyd et al., 2015, Nanotechnology 26:265303). This caused the material to grow to a greater degree in areas where the seed layer was of better quality due to the decomposition, and therefore had the desired selective growth effect. This technique however did not preclude growth in other regions. In the field of 2D materials, there are several reports on the patterned synthesis of MoS2 nanostructures based on the sulfurization of pre-patterned metal oxide or metal seeds (Han et al, 2015, Nat Commun 6:6128). Most notably, MoS2 film properties and grain size can be controlled by controlling the density of MoO3 nanoribbons on the substrate which were then converted in a typical sulfurization process. However, this process still requires careful placement and control of the density of MoO3 nanoribbon precursors and is only compatible with the sulfurization of molybdenum precursors. Furthermore, only the nucleation sites are defined, and the lateral growth and diffusion is not readily controllable.
There has been some selectivity reported for graphene due to theoretical predictions of electronic tuning of properties by changing the width and crystallographic orientation of the edges in a graphene nanoribbon (Nakada et al., 1996, Phys Rev B 54:17945-61; Yazyev, 2013, Ac Chem Res 45:2319-28+C18). Like graphene, two dimensional transition metal dichalcogenide (TMD) nanoribbons are predicted to display extraordinary electronic and magnetic properties. In spite of the predicted extraordinary properties of 2D nanoribbons, bottom-up template synthesis process have been quite limited. Previous works on the templated synthesis of 2D materials have focused on graphene grown from silicon carbide, where electron beam irradiation (Dharmaraj et al., 2013, J Phys Chem 117:19195-202) or crystallographic confinement (Baringhaus et al., 2014, Nature 506:349-54; Sprinkle et al., 2010, Nat Nanotechnol 5:727-31) have been utilized. These techniques, while useful for templated growth of graphene, are limited to a single substrate: SiC. The processes developed in these techniques cannot be generalized to arbitrary substrates or other 2D materials. Extending beyond graphene, recent works have demonstrated thickness control of high quality MoS2 (Jeon et al., 2015, Nanoscale 7:1688-95), but without lateral control of the growth. Therefore it is important to find simplistic techniques to allow for a wide array of 2D materials over a wide variety of substrates.
Thus, there is a need in the art for methods of templated growth of 2D materials. The present invention meets this need.